(1) Field of the Invention
This invention relates to a group communication method, a communication device and a management device, and more particularly, to a group communication method, a communication device and a management device for group communication.
(2) Description of the Related Art
IP multicast communication has been widely known as a technique to simultaneously transmit the same data to a plurality of receiving ends.
For the IP multicast communication, a method where a server selects a multicast group comprising member terminals and transmits data to the group has been proposed (for example, Japanese Patent Application Laid-open No. 2003-134161).
As another technique to simultaneously transmit the same data to a plurality of receiving ends, Push-to-Talk communication has been known, which realizes group communication by half duplex communication.
In the IP multicast communication, a multicast distribution tree is constructed and then multicast data is transmitted. As to the multicast distribution tree, multicast routers are used as routers and connected by unicast between them.
In the Push-to-Talk communication, data is transmitted to the member terminals of a group by unicast.
The above IP multicast service, however, has a drawback in that a network is not easily built because special routers and a unique protocol should be provided on the network.
The Push-to-Talk communication, on the other hand, can realize the service, irrespective of network. However, the unicast communication may cause excessive network traffic when the number of member terminals increases in the group.